This application is based upon Japanese Patent Application Nos. 2000-239858 filed on Aug.8, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention:
This invention relates to a photo-detection sensor, which can be applied to, for example, a photo-detection sensor for a vehicle, and more particularly, applied to a photo-detection sensor for a light control system or a solar radiation sensor for an air conditioner in the vehicle.
2. Related Art:
It has heretofore been known to fabricate a plurality of light receiving elements in one chip (refer to, for example, Japanese Patent Laid-Open No. 03-311084). In case of adopting this structure, it is posed as a problem how the light receiving elements are isolated in order to operate individual light receiving elements independently. Concretely, the crosstalk, between the respective light receiving elements, appear as a drawback. As a method for solving the problem, the inventors of the present invention have supposed that an n-type epitaxial layer is formed on a p-type substrate, that parts of the n-type epitaxial layer are surrounded with p-type regions in order to form islands, and that the light receiving elements are formed in the respective islands. That is, the elements can be made perfectly independent by forming the islands which are reliably isolated by the p-type isolation layers.
Such a construction, however, incurs a drawback that the isolation distance between the elements lengthens so that a chip size is enlarged.
Besides, a drawback appears, which hampers the independent operations of the respective light receiving elements in the case of forming the plurality of light receiving elements within one chip. This drawback is caused by the fact that light projected on the vicinity of the isolation portion between the light receiving elements reaches the light receiving portions of the respective light receiving elements on both the sides because of scattering, thereby influencing on the outputs of the light receiving elements. In this manner, the above construction incurs the drawback that the optical isolation between the light receiving elements worsens.
An object of the present invention is to provide a photo-detection sensor in which individual light receiving elements can be independently operated by a novel construction.
According to first aspect of the present invention, at least one trap region is formed in a part between regions for forming a plurality of light receiving elements, and carriers generated with the projection of light in the light receiving elements are trapped by the trap region. In this way, the crosstalk between adjacent light receiving elements is suppressed, and the respective light receiving elements can be operated independently.
The plurality of light receiving elements are so fabricated that the p-type regions of the respective light receiving elements are formed in the surface layer parts of an n-type region common to the light receiving elements, and that electrodes of the respective elements are arranged in the corresponding p-type regions. Besides, the trap region is formed as a heavily-doped n-type region which is formed in a part of the common n-type region between the adjacent p-type regions. Such a structure is advantageous as explained below. When elements are made independent by forming islands which are isolated by p-type isolation layers, the isolation distance between the elements lengthens to enlarge a chip size. In contrast, according to the present invention, one light receiving element is not disposed in one island, but the plurality of light receiving elements are formed in one island and are isolated by the trap region, whereby the enlargement of the chip size can be avoided.
Further, owing to a structure in which the trap region reaches a buried heavily-doped n-type region, the light receiving elements can be isolated more perfectly.
According to second aspect of the present invention, at least one light shielding film is arranged on a area between regions for forming a plurality of light receiving elements. The light shielding film can avoid the scattering of light projected on an area between the adjacent light receiving elements, and scattered light does not reach the light receiving portions of the light receiving elements on both the sides. As a result, outputs of the light receiving elements are prevented from being influenced by the scattered light. Thus, the light receiving elements are optically isolated, and the respective light receiving elements can be independently operated.
In this way, the crosstalk between the light receiving elements can be suppressed, while the light receiving elements are optically isolated without fail, so that the respective light receiving elements can be independently operated.